I got a letter from my coach lien holder, car has none. It required I purchase my Mexican liability ahead of time, and providing them with info as to dates, destinations, park we were staying at and park contact info.
Letter might become an issue if you had a claim to file.
My insurance carrier, National General, provided collision/comprehensive on the coach for $10, but would not on the Jeep.
We went in with a group of 14 coaches. The first few they asked for vehicle registrations, not sure if they would ask about lein holder permission. When they saw they were dealing with 14 coaches, they stopped asking for registrations. I was halfway back in the pack, only asked if we were bringing in cigarettes or liquor.
We crossed in Lukeville late Feb.